Machinability in terms of quality and productivity is of great concern in a competitive market. CNC milling performance is evaluated in terms of surface roughness, material removal rate, taper and facing. CNC machining is done initially in a number of passes an final end milling is done in a single pass. The most common machining parameters are cutting speed, feed, depth of cut. To have a balance between productivity and quality, the machining parameters need to be optimised.
High speed CNC milling process needs to balance between productivity and quality of the end product. While quality is measured in terms of surface finish, the productivity is measured in terms of material removal rate. Good machinable materials acquire a smooth finish as they can be easily cut with less power. They also cause minimum damage to the tool. If the material has improved material properties then it’s machinablity becomes difficult. Hence improving machinability without sacrificing performance is a challenge.
Predicting the optimal parameters for CNC milling is difficult as the milling process depends on several factors. The important factors relative to the material include the thermal conductivity, toughness, chemical properties and the microstructure of the material. The other important factors are the geometry of the cutting tool and the parameters of CNC milling process.
The aim of this research work is to
•Find the important factors that characterise the best performance of the high speed CNC milling process.
•Using combined Genetic Algorithm and Artificial neutral networks techniques to optimise these high speed CNC milling parameters by identifying the correlation between the factors like feed, depth of cutting and cutting speed.
Based on the correlation of these parameters, the optimal set is to be determined for perfect output parameters like surface roughness and material removal rate. (4) High speed CNC Milling : CNC milling is the most fundamental operation in industrial machining. According to Mike S. Lou et al (1999 ) “The quality of the surface plays a very important role in the performance of milling as a good-quality milled surface significantly improves fatigue strength, corrosion resistance, or creep life. Surface roughness also affects several functional attributes of parts, such as contact causing surface friction, wearing, light reflection, heat transmission, ability of distributing and holding a lubricant, coating, or resisting fatigue”. Speed of the milling depends on the tool size used. If the tool size is smaller, then to avoid breakage of the tool the spindle speed required will be more. For milling with using micro tools the speed range of the spindles may be up to 60,000 rpm ( Datron white paper, 2005). Thus high speed milling involves higher RPM rates with more feed rates and small step overs. The advantage of this high speed is that there is less heating of the parts because of less time for the heat to feedback. The generated heat is 40% due to the friction and 20% due to deformation. For better quality in machining, the low milling force and cooler tools can be used so that the vibration is less. A white paper of DATRON (2005) states that “The high spindle speed reduces the chip load to less than 0.005”. Such a low chip load significantly reduces the forces between the tool and the material. High-speed/low-force machining yields less heat, reduces tool deflection, and allows machining of thinner walled work pieces. This all results in cooler machining, superior surface and edge quality, better accuracy and, as a